468 PRINCIPLES OF CHEMISTRY 



mono-, di-, and tri-chloracetic acids CH. 2 GTCOOH, CHC1/COOH, and 

 CC1 3 'COOH ; they are all, like acetic acid, monobasic. Without enter- 

 ing into the further description of cases of like reaction (they must be 

 looked for in organic chemistry), it is necessary to turn special attention 

 first to the fact that in this manner by an indirect method, carbon 

 compounds (for instance, CC1 4 , C. 2 C1 4 , C (i Cl (! , &c.) are formed, which 

 cannot be obtained directly from the elements, and secondly, that the 

 resulting products of metalepsis, in containing an element which so 

 easily acts on metals as chlorine, give the possibility of attaining a 

 further complexity of molecules for which the original hydrocarbon is 

 often in no way capable. Thus on treating with an alkali (or first 

 with a salt and then with an alkali, or with a basic oxide and water, 

 <kc.) the chlorine forms a salt with its metal, and the hydroxyl radicle 

 takes the place of the chlorine for example, CH 3 'OH is obtained from 

 CHjjOL By the action of metallic derivatives of hydrocarbons for 

 instance, CH 3 Na the chlorine also gives a salt, and the hydrocarbon 

 radicle for instance, CH 3 takes the place of the chlorine. Thus, or 

 in a similar manner, CH 3 'CH 3 or C 2 H 6 is obtained from CH 3 C1 or 

 C 6 H 5 'CH 3 from C 6 H 6 . The products of metalepsis also often react on 

 ammonia, forming hydrochloric acid (and thence NH 4 C1) and an 

 amide ; that is, the product of metalepsis with the ammonia radicle 

 NH. 2 in the place of chlorine. Thus by means of metalepsical substitu- 

 tion a method is found in chemistry for an artificial and general means 

 of the formation of complex carbon compounds from more simple 

 compounds which are often totally incapable of direct reaction. 

 Besides which, this key opened the doors of that secret edifice of the 

 structure of complex organic compounds into which man had up to 

 then feared to enter, supposing it to be the dwelling of the spirits of 

 organisms under the influence of whose magical force that was united 

 which by other means could not be brought together. 26 



26 With the predominance of the representation of compound radicles (this doctrine 

 dates from Lavoisier and Gay-Lussac) in organic chemistry, it was a very important 

 moment in its history when it became possible to gain an insight into the structure of 

 the radicles themselves. It was clear, for instance, that ethyl, C 2 H 5 , or the radicle of 

 common alcohol, C 2 H 5 'OH, passes, without changing, into a number of ethyl derivatives, 

 but its relation to the still simpler hydrocarbons was not clear, and occupied the attent ion 

 of science in the ' forties ' and ' fifties,' Having obtained ethyl hydride, C.^HsH = CoHg, it 

 was looked on as containing the same ethyl, just as methyl hydride, CH 4 = CH3H, was 

 considered as existing in methane. Having obtained free methyl, CH 5 CH5 = C.^H 6 , from 

 it, it was considered as a derivative of methyl alcohol, CH 5 OH, and as only isomeric with 

 ethyl hydride. By means of the products of metalepsis it was proved that this is not a 

 case of isomerism but of strict identity, and it therefore became clear that ethyl is 

 methylated methyl, C 2 H 5 = CH 2 CH 3 . In its time a still greater impetus was -i\( n 1>\ 

 the study of the reactions of monochloracetic acid, CHoCl'COOH, or CO(CH 2 C1)(OH). j 

 Jt appeared that metalepsical chlorine, like the chlorine of chloranhydrides for instance 



